Just to add.. like I thought.. Crutchfield IS expensive.. I just google'd the model number.. and these exact model tube's are going for $250 each on Amazon. $500 total for 500 watts of bass that goes down to 30hz doesn't sound all that bad.
I'm thinking you're right - tubes now are better than prior years. Sadly, people don't realize that - and don't use them nearly as much.Today's tubes are much better than prior years. Although I don't have one in my T I do install them in other vehicles and I can say that the cabin space in our trucks is the right size for a single 10". If you want more then two would really rock it out.
I haven't even looked at audio upgrades for my truck yet, been too busy with all of the exterior things, but if I can find a good spot for a tube I would do one.